Molecules can be illustrated in a variety of ways which can be confusing. Below is a brief lesson on how to read the most common types of chemical diagrams, including the line structures, Lewis structures, and condensed formulas. The line diagram is going to be the only type of diagram used in this website.
Molecules are “bunches” of atoms bonded together. The specific atoms within a molecule are written as the abbreviation of that element, so for example iron is represented by Fe. Bonds between atoms can then be represented as lines connecting them. Fig 1 shows a water molecule, 2 hydrogen atoms are represented by the H symbol and the oxygen is represented by the O symbol, it is clearly illustrated how they are connected using straight lines. Fig 1 is a Lewis diagram.
However in organic chemistry molecules can be incredibly large and take a long time to draw. To shorten the process, chemists created a faster way to write diagrams, this is called the line structure, but can also be referred to as skeletal structures, bond line structures, or line angle structures. The way these diagrams work is by shortening the most commonly found atom (carbon) into a blank space. Carbon atoms also prefer to have 4 bonds at any time so it is assumed in the diagram that if less than 4 bonds are shown to a carbon atom the remainder of the bonds are then bound to hydrogen atoms. Fig 2 shows an example of this shortening, the Lewis structure on the right has the elements fully written and annotated, whereas in the middle each end of a line is implied to be a carbon atom with the appropriate number of hydrogen atoms bonded to it.
Sometimes there may be double or triple bonds connecting atoms represented by two lines, this can be seen in the example second from the top in Fig 2. Sometimes the lack of bonds are shown by annotating the free electrons as dots, but these are unnecessary for the understanding covered in this website, an example of this can be found in the bottom example shown in Fig 2.
The final column on the right side shows the condensed formula, using just the actual elements. In condensed form each new element is represented by a capital letter as some elements have 2 letters, the second letter will always be lowercase, such as iron (Fe) or magnesium (Mg). Numbers then represent the amount of the element mentioned before it, the absence of a number then implies only a single atom.
A video explaining line diagrams can be found here: https://www.youtube.com/watch?v=RuKWQHwJldE
A video explaining chemical formulas can be found here: https://www.youtube.com/watch?v=EoaOaQGCfwE
More types of chemical diagrams not explained in this website can be found here: https://www.chem.ucalgary.ca/courses/351/Carey5th/Ch03/ch3-0-2.html